Many construction and agricultural machines utilise hydraulic actuators to operate various components such as work tools. For example, backhoe loaders and excavators typically have a digging bucket on the end of a two-part articulated arm. The two-part articulated arm may comprise a ‘boom’, which is mounted on the backhoe loader, and a ‘stick’ (also known as a ‘dipper’), which is articulated to the boom and carries the bucket. The movement of the various components may be controlled via hydraulic actuators. Hydraulic fluid is usually directed to the hydraulic actuators, which are typically cylinder-piston arrangements, via flexible hoses and various valves.
It may be useful to detect the position of the hydraulically actuated components of the machine, as this may enable the machines to have features that improve productivity, safety and increase their lifespan. This measurement may be performed in a number of ways, such as measuring the relative rotation of the hydraulic cylinder about a pivot point or comparing signals generated by encoders mounted on the vehicle body and the hydraulically actuated component.
It is also known to measure the stroke of the piston within the hydraulic cylinder to determine the cylinder position. As described in CN-A-201121621, a rotary encoder is mounted at one end of and inside the cylinder. The rotary encoder has a wire which is attached to the piston rod. Movement of the piston, and therefore the piston rod, extends and retracts the wire, enabling the rotary encoder to measure the piston stroke (which is also known as the cylinder stroke) and from that to determine the position of the cylinder. However, in this type of arrangement the cylinder has to be modified to permit this type of arrangement. In particular the length of the cylinder needs to be increased to accommodate the encoder and associated apparatus.
It is an object of the present invention to provide improved apparatus for enabling the position of the cylinder of a hydraulic actuator to be determined.